Finished in 1977, Killer of Sheep is a film by the most important black director in the history of American moving pictures, Charles Burnett. To obtain an adequate understanding of the film—which is set in a black L.A. neighborhood, and is about a sad man who kills sheep for a living—you must watch it much more than once. (Northwest Film Forum, 1515 12th Ave, 329-2629. 7 pm and 9:15 pm, $8/$5 for members, through Sept 15.)